Barbara Kottmeier

Investigating a lethal toxin that was unleashed on a wedding ceremony as a weaponized experiment, Walter uncovers an alarming formula that reveals a link to the Bishop family tree.

Oliver collapses at a charity event and reveals he only has 24 hours to live. Clark and Chloe call Davis for help but his prognosis is grim. Delirious, Oliver flashes back to when he was stranded on an island and first learned how to use a bow and arrow. He also recalls meeting Tess for the first time on that island after she had been kidnapped by a drug runner. Meanwhile, Chloe decides to use her new powers to help save Oliver, shocking Clark.

This crossover episode of "Life Unexpected" brings "One Tree Hill" characters Haley and Mia to a music festival, sponsored by a Portland radio station and hosted by Ryan. At the concert, Haley and Cate meet and discover that they have incredibly similar pasts.

Lewis asks Marti out but she turns him down. Alice tells Lewis she will stop taking drugs if he helps her get back in shape as a flier; then, after a sweaty workout, the two end up having sex. Meanwhile, Savannah takes Dan to her parents' house for dinner and a fight erupts after Savannah's mom (guest star Teryl Rothery - Stargate SG-I, Kyle XY, The Guard) demands that she stop seeing Dan. Wanda convinces Marti to give Lewis a chance so she tells him she's ready to date - but he has second thoughts.

Eight out of the original 25 suspects strive to be one of the few survivors as all answers are revealed, on the season finale.